This invention relates generally to systems capable of initiating polymerization. More specifically, the invention relates to initiator systems comprising (1) a complexed initiator and (2) decomplexers. The invention further relates to the use of these systems for initiating polymerization, as well as kits, bonding compositions, and polymerized compositions made therewith, coated substrates prepared therefrom, bonded articles prepared therefrom, and methods of preparing such bonded articles.
Systems for initiating the polymerization of monomers to make adhesive compositions are known in the art. U.S. Pat. Nos. 5,106,928, 5,286,821, and 5,310,835 to Skoultchi et al., for example, describe two-part initiator systems for initiating the polymerization of acrylic monomers. The first part of these two-part systems includes a stable organoborane amine complex and the second part includes an activator. The activator liberates the organoborane compound by removing the amine group, thereby allowing the organoborane compound to initiate the polymerization process. Activators are also sometimes referred to as liberators or decomplexers.
U.S. Pat. No. 5,286,821 to Skoultchi describes that suitable activators for liberating the organoborane compound include aldehydes having the general structure:
Rxe2x80x94(CHO)x
wherein R is an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms and x is 1 to 2. Examples include benzaldehyde; o-, m-, p-nitrobenzaldehyde; 2,4-dichlorobenzaldehyde; p-tolylaldehyde; and 3-methoxy-4 hydroxybenzaldehyde.
U.S. Pat. Nos. 5,310,835 and 5,106,928 describes that suitable activators for liberating the organoborane compound also include organic acids having the structure:
Rxe2x80x94COOH
wherein R is H, an alkyl group, or an alkenyl group having 1 to 8 carbon atoms. Examples include acrylic acid, methacrylic acid, benzoic acid, and p-methoxybenzoic acid.
Fujisawa, Imai, and Mashuhara also describe a system for initiating the polymerization of methyl methacrylate (See, Reports of the Institute for Medical and Dental Engineering, vol. 3, page 64 (1969)). The system comprises a trialkylborane amine complex and an activator such as the chloride of methacrylic or n-butane sulfonic acid, terephthalic acid chloride, benzoyl chloride, p-toluene sulfonic acid chloride, benzene sulfonic acid chloride, methane sulfonic acid chloride, toluene diisocyanate, adipic acid chloride, o-tolyl isocyanate, acetyl chloride, and acetic acid anhydride. The initiator system is reportedly useful in providing fast curing resins for dental applications.
One disadvantage of some of the aforementioned activators, however, is the relatively high odor of the activators and the composition in which they are used. Furthermore, another disadvantage of some of these activators is the relatively high level of mobile activator-amine reaction products (i.e., activator-amine constituents) in resulting adhesives. Typically, activators liberate the organoborane compound by bonding (either covalently or ionically) to the amine to form an activator-amine constituent. Most activator-amine constituents remain in the adhesive composition as mobile constituents that are not incorporated into the polymerized adhesive per se. In general, mobile constituents in adhesive compositions may cause performance problems when, for example, they migrate to the surface of the adhesive thereby disrupting the bond interface. Mobile constituents are also susceptible to attack by solvents, thereby making the adhesive composition less suitable for applications where exposure to solvents is unavoidable.
Recently, it has been disclosed that certain activators are useful for reducing the level of mobile constituents in adhesive compositions polymerized therewith. For example, PCT Publication No. W097/07171 discloses bireactive decomplexers preferably comprising at least one free-radically polymerizable group and at least one amine-reactive group, preferably an isocyanate group, in the same molecule. The bireactive decomplexers are capable of forming a covalent bond with both acrylic monomers and the amine portion of the organoborane amine complex. Accordingly, the decomplexer is capable of covalently bonding to the liberated amine in the system and also reacting into the adhesive per se.
PCT Publication No. WO97/17383 discloses decomplexers comprising at least one anhydride group. Preferred anhydrides have one of the following structures: 
wherein R1 and R2 may independently be an aliphatic group; a cycloaliphatic group; or an aromatic group. R3 is a divalent organic radical that completes a cyclic structure with the anhydride group. It is further preferred that the decomplexer comprises at least one free radically polymerizable group that is capable of forming a covalent bond with an acrylic monomer, such that the decomplexer-amine reaction product is capable of forming covalent bonds with acrylic monomer(s) and can be incorporated into the polymerized adhesive per se.
Such previous systems, however, may experience instability when exposed to hydroxy-functional materials, such as water and 2-hydroxyethyl methacrylate. For example, such hydroxy-functional materials may react with the isocyanate and anhydride functional groups on the decomplexers, resulting in a reduced amount of decomplexer available for activating the initiator systems. Thus, a need exists for further initiator systems that provide improved adhesive compositions, while maintaining low levels of mobile constituents and improved solvent resistance. It is also desirable to provide initiator systems that have relatively low odor.
Initiator systems of the present invention include both a complexed initiator (e.g., organoborane amine complex) and a carboxylic acid decomplexer. For example, dicarboxylic acid decomplexer, carboxylic acid ester decomplexers, and monocarboxylic acid decomplexers (preferably those comprising an alkyl group having at least nine carbon atoms for low odor compositions) are useful in the present invention.
In one embodiment, an initiator system of the present invention, comprises:
a complexed initiator; and
a decomplexer having a structure represented by (I) or (II): 
wherein:
R1 is selected from the group consisting of hydrogen, a monovalent organic group, and a multivalent organic group;
R2 is a multivalent organic group;
R3 is selected from the group consisting of hydrogen and a monovalent organic group;
R is a monovalent organic group comprising an alkyl group having at least nine carbon atoms, preferably at least 15 carbon atoms;
m is an integer of 0-2; and
n is an integer greater than or equal to one.
In another embodiment, an initiator system of the present invention comprises:
a complexed initiator;
a carboxylic acid decomplexer; and
a second decomplexer.
This second decomplexer may be, for example, another carboxylic acid decomplexer, or it may be, for example, an anhydride decomplexer. Particularly preferred anhydride decomplexers are methacrylic anhydride, succinic anhydride, maleic anhydride, and glutaric anhydride.
The decomplexers are useful in kits that comprise a polymerizable composition (which includes the decomplexer(s) and at least one polymerizable monomer) and an initiator component (which includes the complexed initiator and an optional diluent) for polymerizing the polymerizable composition. Such kits are useful for bonding low surface energy substrates. For ease of application, the kits can further comprise a multi-part dispenser.
A method of initiating polymerization of at least one polymerizable monomer comprises the steps of:
providing at least one monomer;
blending the at least one monomer with an initiator system of the present invention; and
initiating polymerization of the at least one monomer.
Once the parts of the kit are mixed together, bonding compositions are obtained. The compositions can be at least partially coated onto a substrate, particularly low surface energy substrates.
Once polymerized, a polymerized composition is obtained. The polymerized composition can be, for example, at least partially coated on a substrate or can be used to adhere a first and second substrate together in a bonded article.